Polyester resins are well-known in the art. The polyester resins are used to form thermoset resins compositions which are especially useful in various molding applications. In particular, the reaction injection molding (RIM) process uses such resin compositions to make resin-reinforced fiberglass structures for use in automobile applications. The unsaturated polyesters resins are generally the poly condensation products of di-or poly-carboxylic acids or their anhydrides and di-or poly-hydroxylated alcohols or alkylene oxides. The unsaturated polyester resins are usually crosslinked through their double bonds with a compatible monomer also containing ethylenic unsaturation. The cross-linked resins are thus thermoset and when fully cured are insoluble and infusible. For example, the Dunnavant et al., U.S. Pat. No. 4,374,229 assigned to the Ashland Oil Co., discloses a moldable reactive acrylic resin based on logiomeric polyesters which are structurally linked through a urethane residue. The composition contains polyester segments containing internal ethylenic unsaturation terminally joined to one another through polyurethane linkages. Each of the polyesters segments possess end groups containing vinyl unsaturation. The compositions are copolymerized with a vinyl or polyallyl crosslinking agent.
Dunnavant et al. does not, however, suggest the achievement of low viscosity, hydroxylated, partially aminated polyester resins which are compatible with a polyisocyanate and which have an increase in functionality due to additional hydroxyl groups incorporated into the resin backbone.